A "divisive" topic is one that:

A topic described as "divisive" often creates strong differences in opinion among people, leading to disagreements or conflict. This term is typically used in contexts where views are sharply split, causing some individuals to take sides. When certain subjects provoke passionate reactions either for or against them, they can foster division rather than unity, illustrating why the term is associated with conflict.

The other options do not match the meaning of "divisive." A topic that brings everyone together would be seen as unifying, while one that is universally popular does not evoke conflict but rather widespread agreement. Lastly, a topic that is rarely discussed lacks the necessary engagement and debate that typically characterize a divisive issue.